This invention relates to a method and apparatus for impregnating a web of fibrous material. In one of the more specific aspects of the invention, a foamed or air-diluted binder is supplied to the surface of the fibrous material and a source of vacuum is used to draw the binder into the fibrous material to impregnate the material.
Resinous binder materials have been applied in the past to fibrous material to join the fibrous material into a web and to increase the strength of the collected fibrous material. In the manufacture of organic and inorganic fibrous webs, the fibrous material is formed into fibers and deposited on a collection surface. As the fibers are being deposited and collected on the surface a binder material is normally applied to the fibers. The application of the binder in this manner results in a sufficient amount of the binder coming into contact with the junctures of the fibers to hold the fibers together in a fibrous web. However, the amount of binder that can be applied to the fibrous material is severely limited in this application. If too much binder material is applied to the fibers as they are being deposited the fibers will lump together and form a solid mass on the conveyor. The application of too much binder material can also result in too much binder material being applied to the collection surface. This excess binder material can clog up the collection apparatus and result in a serious maintenance problem. In addition, it is very difficult to control the uniformity of the application of the binder material when such binder material is being applied to fibers as the fibers are formed and collected. Thus, the application of binder material to fibers as they are being formed and collected will not result in the formation of a uniformly impregnated fibrous web.
Webs of fibrous material can also be formed by combining virgin and reclaimed fibers. In this process the fibers are passed through a fiber reducing and opening apparatus where the fibers are broken down and combined. The binder material is applied after the fibers have been broken down and combined. After the binder has been applied the fibers are collected in the form of a web. There is normally sufficient contact between the binder and the fibers to hold the fibers into a web when using this process. However, the amount of binder material that can be applied to the fibers in this process is limited. In addition, the uniformity of the binder on the fibers in the web is very difficult to control. Therefore, the end uses of the fibrous web formed by this process are limited by the amount and uniformity of the binder that can be applied to the fibers that form the web.
If it is desired to increase the amount of binder in a fibrous web the additional binder is usually added after the web is formed. The fibrous web, that contain enough binder material to hold the fibers into a web, is supplied with additional liquid binder. The liquid binder is worked into the fibrous web by passing the web through the nip of two opposed rolls. The rolls are positioned to push the liquid binder material into the fibrous web. However, the rolls tend to break or damage the fibers in the fibrous web. Therefore, the rolls alter the properties of the fibrous web. In addition, the rolls do not uniformly distribute the binder material in the fibrous web. The fibers comprising the web are deposited in the web in such a random fashion that the resistance to flow to the liquid binder material varies throughout the web. Therefore, the fibrous web is not uniformly impregnated by this process.
Accordingly, there is a need in the art to develop a method and apparatus for impregnating fibrous webs that can uniformly and completely impregnate the web.